Induction of stem cell gene expression in adult human fibroblasts without transgenes.

Reprogramming of differentiated somatic cells into induced pluripotent stem (iPS) cells has potential for derivation of patient-specific cells for therapy as well as for development of models with which to study disease progression. Derivation of iPS cells from human somatic cells has been achieved by viral transduction of human fibroblasts with early developmental genes. Because forced expression of these genes by viral transduction results in transgene integration with unknown and unpredictable potential mutagenic effects, identification of cell culture conditions that can induce endogenous expression of these genes is desirable. Here we show that primary adult human fibroblasts have basal expression of mRNA for OCT4, SOX2, and NANOG. However, translation of these messages into detectable proteins and their subcellular localization depends on cell culture conditions. Manipulation of oxygen concentration and FGF2 supplementation can modulate expression of some pluripotency related genes at the transcriptional, translational, and cellular localization level. Changing cell culture condition parameters led to expression of REX1, potentiation of expression of LIN28, translation of OCT4, SOX2, and NANOG, and translocation of these transcription factors to the cell nucleus. We also show that culture conditions affect the in vitro lifespan of dermal fibroblasts, nearly doubling the number of population doublings before the cells reach replicative senescence. Our results suggest that it is possible to induce and manipulate endogenous expression of stem cell genes in somatic cells without genetic manipulation, but this short-term induction may not be sufficient for acquisition of true pluripotency. Further investigation of the factors involved in inducing this response could lead to discovery of defined culture conditions capable of altering cell fate in vitro. This would alleviate the need for forced expression by transgenesis, thus eliminating the risk of mutagenic effects due to genetic manipulation.